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| United States Patent |
5,574,599
|
|
Hoshi
, et al.
|
November 12, 1996
|
Zoom lens and zooming method
Abstract
A zoom lens comprising, from front to rear, a first lens unit of negative
refractive power, a second lens unit of positive refractive power and a
third lens unit of negative refractive power, wherein during zooming from
the wide-angle end to the telephoto end, at least the second lens unit and
the third lens unit move axially forward, and the following conditions are
satisfied:
##EQU1##
where f.sub.W and f.sub.T are the shortest and longest focal lengths of
the entire system, respectively, f.sub.1 is the focal length of the first
lens unit, f.sub.2 is the focal length of the second lens unit, and
f.sub.3 is the focal length of the third lens unit.
| Inventors:
|
Hoshi; Kouji (Kanagawa-ken, JP);
Itoh; Yoshinori (Kanagawa-ken, JP);
Nishio; Akihiro (Kanagawa-ken, JP)
|
| Assignee:
|
Canon Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
153024 |
| Filed:
|
November 16, 1993 |
Foreign Application Priority Data
| Nov 18, 1992[JP] | 4-333593 |
| Nov 19, 1992[JP] | 4-310281 |
| Apr 14, 1993[JP] | 5-111058 |
| Current U.S. Class: |
359/689; 359/683 |
| Intern'l Class: |
G02B 015/14 |
| Field of Search: |
359/683,689,676,686
|
References Cited
U.S. Patent Documents
| 4936661 | Jun., 1990 | Betensky et al. | 350/423.
|
| 5218478 | Jun., 1993 | Itoh | 359/692.
|
| 5274504 | Dec., 1993 | Itoh | 359/676.
|
| Foreign Patent Documents |
| 63-25613 | Feb., 1988 | JP.
| |
| 63-271214 | Nov., 1988 | JP.
| |
| 64-72114 | Mar., 1989 | JP.
| |
| 2238417 | Sep., 1990 | JP.
| |
| 2238418 | Sep., 1990 | JP.
| |
Primary Examiner: Sugarman; Scott J.
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto
Claims
What is claimed is:
1. A zoom lens comprising:
a front lens unit of negative refractive power;
an intermediate lens unit of positive refractive power; and
a rear lens unit of negative refractive power,
zooming being performed by varying a separation between said front lens
unit and said intermediate lens unit and a separation between said
intermediate lens unit and said rear lens unit, and said zoom lens
satisfying the following conditions:
##EQU6##
where f.sub.W is the overall focal length of the entire lens system in a
wide-angle end, f.sub.T is the overall focal length of the entire lens
system in a telephoto end, f.sub.1 is the focal length of said front lens
unit, f.sub.2 is the focal length of said intermediate lens unit, and
f.sub.3 is the focal length of said rear lens unit.
2. A zoom lens according to claim 1, wherein during zooming from the
wide-angle end to the telephoto end, at least said intermediate lens unit
and said rear lens unit move forward.
3. A zoom lens according to claim 1, satisfying the following conditions:
0.4<l.sub.1W /f.sub.W <0.8
0.21<l.sub.2W /f.sub.W <0.37
0.55<f.sub.12W /f.sub.W <0.92
where l.sub.1W is an axial air separation between said front lens unit and
said intermediate lens unit in the wide-angle end, l.sub.2W is an axial
air separation between said intermediate lens unit and said rear lens unit
in the wide-angle end, and f.sub.12W is the overall focal length of said
front lens unit and said intermediate lens unit in the wide-angle end.
4. A zoom lens according to claim 1 or 3, wherein said front lens unit
includes, from front to rear, at least one negative lens having a concave
surface facing an image side and at least one positive lens having a
convex surface facing an object side, and said intermediate lens unit
includes at least two lens surfaces of convex curvature facing the object
side and at least one lens surface of convex curvature facing the image
side, a frontmost lens in said intermediate lens unit being a positive
lens, and said rear lens unit includes at least one lens surface of
concave curvature facing the object side.
5. A zoom lens comprising:
a front lens unit of negative refractive power, an intermediate lens unit
of positive refractive power and a rear lens unit of negative refractive
power, zooming being performed by varying a separation between said front
lens unit and said intermediate lens unit and a separation between said
intermediate lens unit and said rear lens unit, and said zoom lens
satisfying the following conditions:
0.4<l.sub.1W /f.sub.W <0.8
0.21<l.sub.2W /f.sub.W <0.37
0.55<f.sub.12W /f.sub.W <0.92
where f.sub.W is the overall focal length in a wide-angle end of the
entire lens system, l.sub.1W is an axial air separation between said front
lens unit and said intermediate lens unit in the wide-angle end, l.sub.2W
is an axial air separation between said intermediate lens unit and said
rear lens unit in the wide-angle end, and f.sub.12W is the overall focal
length of said front lens unit and said intermediate lens unit in the
wide-angle end.
6. A zoom lens according to claim 5, wherein during zooming from the
wide-angle end to a telephoto end, said intermediate lens unit and said
rear lens unit move forward.
7. A zoom lens comprising:
a front lens unit of negative refractive power, an intermediate lens unit
of positive refractive power and a rear lens unit of negative refractive
power in order from an object side, zooming being performed by varying a
separation between said front lens unit and said intermediate lens unit
and a separation between said intermediate lens unit and said rear lens
unit, and said zoom lens satisfying the following condition:
1.0<.vertline.f.sub.3 .vertline./.vertline.f.sub.1 .vertline.<2.0
where f.sub.1 is the focal length of said front lens unit and f.sub.3 is
the focal length of said rear lens unit.
8. A zoom lens according to claim 7, wherein during zooming from a
wide-angle end to a telephoto end, said intermediate lens unit and said
rear lens unit move forward.
9. A zoom lens according to claim 7, satisfying the following condition:
0<(e.sub.1W -e.sub.1T)/(e.sub.2W -e.sub.2T)<10
where e.sub.1W and e.sub.1T are intervals between a principal point of said
front lens unit and a principal point of said intermediate lens unit in a
wide-angle end and a telephoto end, respectively, and e.sub.2W and
e.sub.2T are intervals between the principal point of said intermediate
lens unit and a principal point of said rear lens unit in the wide-angle
end and the telephoto end, respectively.
10. A zoom lens according to claim 7 or 9, satisfying the following
condition:
##EQU7##
where f.sub.12W and f.sub.12T are the overall focal lengths of said front
lens unit and said intermediate lens unit in the wide-angle end and the
telephoto end, respectively, and f.sub.W and f.sub.T are the focal lengths
of the entire system in the wide-angle end and the telephoto end,
respectively.
11. A zoom lens comprising:
a front lens unit of negative refractive power, an intermediate lens unit
of positive refractive power and a rear lens unit of negative refractive
power, zooming being performed by varying a separation between said front
lens unit and said intermediate lens unit and a separation between said
intermediate lens unit and said rear lens unit, and said zoom lens
satisfying the following condition:
##EQU8##
where f.sub.12W and f.sub.12T are the overall focal lengths of said front
lens unit and said intermediate lens unit in a wide-angle end and a
telephoto end, respectively, and f.sub.W and f.sub.T are the focal lengths
of the entire system in the wide-angle end and the telephoto end,
respectively.
12. A zoom lens according to claim 11, wherein during zooming from the
wide-angle end to the telephoto end, said intermediate lens unit and said
rear lens unit move forward.
13. A zoom lens comprising:
a front lens unit of negative refractive power, an intermediate lens unit
of positive refractive power and a rear lens unit of negative refractive
power, zooming being performed by varying a separation between said front
lens unit and said intermediate lens unit and a separation between said
intermediate lens unit and said rear lens unit, and said zoom lens
satisfying the following conditions:
##EQU9##
where f.sub.1 is the focal length of said front lens unit, f.sub.W and
f.sub.T are the focal lengths of the entire system in a wide-angle end and
a telephoto end, respectively, and Y is the diagonal length of an
effective image frame.
14. A zoom lens according to claim 13, wherein during zooming from the
wide-angle end to the telephoto end, said intermediate lens unit and said
rear lens unit move forward in such relation that the separation between
said front lens unit and said intermediate lens unit decreases and the
separation between said intermediate lens unit and said rear lens unit
decreases.
15. A zoom lens according to claim 13 or 14, satisfying the following
condition:
0.4<.vertline.f.sub.1 .vertline./Y<0.7.
16. A zoom lens according to claim 15, satisfying the following condition:
0.2<.vertline.f.sub.2 /f.sub.3 .vertline.<0.8
where f.sub.2 is the focal length of said intermediate lens unit, and
f.sub.3 is the focal length of said rear lens unit.
17. A zoom lens according to claim 13, wherein said intermediate lens unit
has a stop arranged therein, and asphere is applied to at least one lens
surface on the object side of said stop.
18. A zooming method for a zoom lens, said zoom lens having, from front to
rear, a first lens unit of negative refractive power, a second lens unit
of positive refractive power and a third lens unit, comprising the steps
of moving two lens units of said first, second and third lens units in
unison to perform a first zooming operation from a wide-angle end to a
medium focal length position, and, after that, taking said two lens units
out of unison and moving at least one lens unit of said two lens units to
perform a second zooming operation from the medium focal length position
to a telephoto end,
said method satisfying at least one of the following conditions:
-0.5<(e1T-e1M)/(fT-fM)<0.1
-0.5<(e2T-e2M)/(fT-fM)<0.1
where, as said first zooming operation shifts to said second zooming
operation, e1M is a principal point interval between said first lens unit
and said second lens unit, e2M is a principal point interval between said
second lens unit and said third lens unit, and fM is the focal length of
the entire system; e1T is a principal point interval in the telephoto end
between said first lens unit and said second lens unit, e2T is a principal
point interval in the telephoto end between said second lens unit and said
third lens unit and fT is the focal length of the entire system in the
telephoto end.
19. A zooming method for a zoom lens, said zoom lens having, from front to
rear, a first lens unit of negative refractive power, a second lens unit
of positive refractive power and a third lens unit, in which, as zooming
is performed by moving said first, second and third lens unit, two lens
units of said first, second and third lens units are moved in unison to
perform a first zooming operation from a wide-angle end to a medium focal
length position and, after that, said two lens units are taken out of
unison and moved in differential relation to perform a second zooming
operation from the medium focal length position to a telephoto end,
said method satisfying at least one of the following conditions:
-0.5<(e1T-e1M)/(fT-fM)<0.1
-0.5<(e2T-e2M)/(fT-fM)<0.1
where, as said first zooming operation shifts to said second zooming
operation, e1M is a principal point interval between said first lens unit
and said second lens unit, e2M is a principal point interval between said
second lens unit and said third lens unit, and fM is the focal length of
the entire system; e1T is a principal point interval in the telephoto end
between said first lens unit and said second lens unit, e2T is a principal
point interval in the telephoto end between said second lens unit and said
third lens unit and fT is the focal length of the entire system in the
telephoto end.
20. A zooming method for the zoom lens according to claim 19, wherein said
first zooming operation is performed by moving either said first lens unit
and said third lens unit in unison, or said first lens unit and said
second lens unit in unison, or said second lens unit and said third lens
unit in unison.
21. A zooming method for the zoom lens according to claim 20, wherein said
first lens unit, said second lens unit and said third lens unit are moved
all forward to perform said first zooming operation and said second
zooming operation.
22. A zooming method for a zoom lens, said zoom lens having, from front to
rear, a first lens unit of negative refractive power, a second lens unit
of positive refractive power and a third lens unit, comprising the steps
of moving said first, second and third lens units to perform a first
zooming operation and, after that, while keeping stationary at least one
lens unit of said first lens unit and said third lens unit, moving said
second lens unit to perform a second zooming operation,
said method satisfying the following conditions:
0<fW(1/f1+2/f2+1/f3)<4
0<f23/fT<0.9
where fi is the focal length of the i-th lens unit, f23 is the overall
focal length of said second lens unit and said third lens unit in an
arbitrary zooming position, and fW and fT are the focal lengths of the
entire system in a wide-angle end and a telephoto end, respectively.
23. A zooming method for the zoom lens according to claim 22, wherein said
first lens unit, said second lens unit and said third lens unit are moved
all forward to perform the first zooming operation, and said second lens
unit is moved forward to perform the second zooming operation.
24. A zooming method for the zoom lens according to claim 23, satisfying at
least one of the following conditions:
-0.5<(e1T-e1M)/(fT-fM)<0.1
-0.5<(e2T-e2M)/(fT-fM)<0.1
where, as said first zooming operation shifts to said second zooming
operation, e1M is a principal point interval between said first lens unit
and said second lens unit, e2M is a principal point interval between said
second lens unit and said third lens unit, and fT is the focal length of
the entire system; e1T is a principal point interval in the telephoto end
between said first lens unit and said second lens unit, e2T is a principal
point interval in the telephoto end between said second lens unit and said
third lens unit, fT is the focal length of the entire system in the
telephoto end.
25. A zooming method for a zoom lens, said zoom lens having, from front to
rear, a first lens unit of negative refractive power, a second lens unit
of positive refractive power and a third lens unit, comprising the steps
of moving said second lens unit, while keeping stationary at least one
lens unit of said first lens unit and said third lens unit, to perform a
first zooming operation, and after that, moving said first, second and
third lens units to perform a second zooming operation,
said method satisfying the following conditions:
0<fW(1/f1+2/f2+1/f3)<4
said method satisfying the following conditions:
0<fW(1/f1+2/f2+1/f3)<4
0<f23/fT<0.9
where fi is the focal length of the i-th lens unit, f23 is the overall
focal length of said second lens unit and said third lens unit in an
arbitrary zooming position, fW and fT are the focal lengths of the entire
system in a wide-angle end and a telephoto end, respectively.
26. A zooming method for the zoom lens according to claim 25, wherein said
first lens unit and said second lens unit in unison and said third lens
unit in differential relation move all forward to perform the second
zooming operation.
27. A zooming method for the zoom lens according to claim 26, satisfying at
least one of the following conditions:
-0.5<(e1T-e1M)/(fT-fM)<0.1
-0.5<(e2T-e2M)/(fT-fM)<0.1
where as said first zooming operation shifts to said second zooming
operation, e1M is a principal point interval between said first lens unit
and said second lens unit, e2M is a principal point interval between said
second lens unit and said third lens unit, and fM is the focal length of
the entire system; e1T is a principal point interval in the telephoto end
between said first lens unit and said second lens unit, e2T is a principal
point interval in the telephoto end between said second lens unit and said
third lens unit, and fT is the focal length of the entire system in the
telephoto end.
28. A zooming method for a zoom lens, said zoom lens having, from front to
rear, a first lens unit of negative refractive power, a second lens unit
of positive refractive power and a third lens unit, comprising the steps
of, as zooming is performed by moving said first, second and third lens
units, performing a first zooming operation from a wide-angle end to a
medium focal length position by moving said first, second and third lens
units in differential relation, and after that, performing a second
zooming operation from the medium focal length position to a telephoto end
by moving two lens units of said first, second and third lens units in
unison,
said method satisfying at least one of the following conditions:
-0.5<(e1T-e1M)/(fT-fM)<0.1
-0.5<(e2T-e2M)/(fT-fM)<0.1
where, as said first zooming operation shifts to said second zooming
operation, e1M is a principal point interval between said first lens unit
and said second lens unit, e2M is a principal point interval between said
second lens unit and said third lens unit, and fM is the focal length of
the entire system; e1T is a principal point interval in the telephoto end
between said first lens unit and said second lens unit, e2T is a principal
point interval in the telephoto end between said second lens unit and said
third lens unit, and fT is the focal length of the entire system in the
telephoto end.
29. A zooming method for the zoom lens according to claim 28, wherein said
first, second and third lens units move all forward to perform the first
zooming operation and the second zooming operation.
30. A zooming method for the zoom lens according to claim 29, wherein said
second zooming operation is performed by moving either said first lens
unit and said third lens unit in unison, or said first lens unit and said
second lens unit in unison, or said second lens unit and said third lens
unit in unison.
31. A zoom lens comprising:
a front lens unit of negative refractive power;
an intermediate lens unit of positive refractive power; and
a rear lens unit of negative refractive power,
zooming being performed by varying a separation between said front lens
unit and said intermediate lens unit and a separation between said
intermediate lens unit and said rear lens unit, and said zoom lens
satisfying the following conditions:
##EQU10##
where f.sub.W is the overall focal length of the entire lens system in a
wide-angle end, f.sub.T is the overall focal length of the entire lens
system in a telephoto end, f.sub.1 is the focal length of said front lens
unit, f.sub.3 is the focal length of said rear lens unit, and l.sub.1W is
an axial air separation between said front lens unit and said intermediate
lens unit in the wide-angle end.
32. A zoom lens comprising:
a front lens unit of negative refractive power;
an intermediate lens unit of positive refractive power; and
a rear lens unit of negative refractive power including a positive single
lens and a negative single lens disposed just behind said positive single
lens,
zooming being performed by varying a separation between said front lens
unit and said intermediate lens unit and a separation between said
intermediated lens unit and said rear lens unit, and said zoom lens
satisfying the following conditions:
##EQU11##
where f.sub.W is the overall focal length of the entire lens system in a
wide-angle end, f.sub.T is the overall focal length of the entire lens
system in a telephoto end, f.sub.1 is the focal length of said front lens
unit, and l.sub.1W is an axial air separation between said front lens unit
and said intermediate lens unit in the wide-angle end.
33. A zoom lens comprising:
a front lens unit of negative refractive power including a plurality of
lenses separated from each other by respective air spaces;
an intermediate lens unit of positive refractive power; and
a rear lens unit of negative refractive power,
zooming being performed by varying a separation between said front lens
unit and said intermediate lens unit and a separation between said
intermediate lens unit and said rear lens unit, and said zoom lens
satisfying the following conditions:
##EQU12##
where f.sub.W is the overall focal length of the entire lens system in a
wide-angle end, f.sub.T is the overall focal length of the entire lens
system in a telephoto end, f.sub.1 is the focal length of said front lens
unit, and l.sub.1W is an axial air separation between said front lens unit
and said intermediated lens unit in the wide-angle end.
34. A zoom lens according to claim 33, wherein said intermediate lens unit
consists of four lenses or less.
35. A zoom lens according to claim 33, wherein said intermediate lens unit
includes a positive lens sub-unit and a negative lens disposed just behind
said positive lens sub-unit.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to zoom lenses suited to be used in photographic
cameras or video cameras and, more particularly, to a zoom lens which has
a front lens unit of negative refractive power, or is of the so-called
"negative lead" type, while still permitting minimization of the size of
the lens system to be achieved.
2. Description of the Related Art
The zoom lenses of the negative lead type with size at a minimum have been
disclosed in Japanese Laid-Open Patent Applications No. Sho 63-25613 and
No. Hei 2-238417, for example. Each of these zoom lenses comprises, from
front to rear, a first lens unit of negative refractive power, a second
lens unit of positive refractive power and a third lens unit of negative
refractive power, with zooming being performed by varying the separations
between the lens units. The use of such a type has made it possible to
realize a minimization of size over the minus-plus form of the 2-unit type
zoom lens which had so far been well known.
The zoom lenses each composed of three lens units having negative, positive
and negative refractive powers are described also in Japanese Laid-Open
Patent Applications No. Sho 63-271214, No. Sho 64-72114 and No. Hei
2-238418 and U.S. Pat. No. 4,936,661.
However, the above-described conventional examples of the minus-plus-minus
form of the 3-unit type zoom lens, despite the total length of the entire
lens system being shortened from that of the minus-plus form of the 2-unit
type zoom lens, have the disadvantage that they are bulky from the point
of view of the outer diameter of the lens.
Meanwhile, with the negative lead type of zoom lens it is, in general,
relatively easy to increase the maximum image angle. For this reason, it
is expected to be used as the lens system for the panorama photography in
recent years.
To achieve widening of the image angle to 90.degree. or more in such a
manner that the optical performance is maintained well over the entire
area of the image frame, however, it is necessary to set forth proper
rules of design of the lens units in terms of the refractive power
arrangement, etc. If these rules are improper, the variation with zooming
of aberrations is caused to increase. The resultant aberrations could not
be corrected well even if the number of lens elements is increased, making
it difficult to obtain a high optical performance throughout the entire
zooming range.
In such zoom lenses, on the other hand, there has been a growing demand for
a much desired increase of the zoom ratio. But, to keep the positions of
the three lens units at a high accuracy as they move in differential
relation to one another, the mounting mechanism for the lens units and the
zooming mechanism tend to become complex in structure and large in size.
SUMMARY OF THE INVENTION
An aspect of the present invention is to provide a zoom lens of the
negative lead type having a high range with good performance.
Another aspect of the invention is to provide a zoom lens which is not only
short in the total length but also shortened in the outer diameter.
A further aspect of the invention is to provide a zoom lens of widened
image angle, while still maintaining high image quality.
A still further aspect of the invention is to extend the zooming range of
the conventional 3-unit type of zoom lens or its modified type of zoom
lens.
These and other aspects of the invention will become apparent from the
following description of the embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a lens block diagram of the numerical example 1 of the invention.
FIG. 2 is a lens block diagram of the numerical example 2 of the invention.
FIG. 3 is a lens block diagram of the numerical example 3 of the invention.
FIG. 4 is a lens block diagram of the numerical example 4 of the invention.
FIG. 5 is a lens block diagram of the numerical example 5 of the invention.
FIG. 6 is a lens block diagram of the numerical example 6 of the invention.
FIG. 7 is a lens block diagram of the numerical example 7 of the invention.
FIG. 8 is a lens block diagram of the numerical example 8 of the invention.
FIGS. 9(A)(1)-9(A)(3) and 9(B)(1)-9(B)(3) are graphic representations of
the various aberrations of the numerical example 1.
FIGS. 10(A)(1)-10(A)(3) and 10(B)(1)-10(B)(3) are graphic representations
of the various aberrations of the numerical example 2.
FIGS. 11(A)(1)-11(A)(3) and 11(B)(1)-11(B)(3) are graphic representations
of the various aberrations of the numerical example 3.
FIGS. 12(A)(1)-12(A)(3) and 12(B)(1)-12(B)(3) are graphic representations
of the various aberrations of the numerical example 4.
FIGS. 13(A)(1)-13(A)(3) and 13(B)(1)-13(B)(3) are graphic representations
of the various aberrations of the numerical example 5.
FIGS. 14(A)(1)-14(A)(3) and 14(B)(1)-14(B)(3) are graphic representations
of the various aberrations of the numerical example 6.
FIGS. 15(A)(1)-15(A)(3) and 15(B)(1)-15(B)(3) are graphic representations
of the various aberrations of the numerical example 7.
FIGS. 16(A)(1)-16(A)(3) and 16(B)(1)-16(B)(3) are graphic representations
of the various aberrations of the numerical example 8.
FIGS. 17(A), 17(B) and 17(C) are lens block diagrams of the numerical
example 9 of the invention.
FIGS. 18(A), 18(B) and 18(C) are lens block diagrams of the numerical
example 10 of the invention.
FIGS. 19(A), 19(B) and 19(C) are lens block diagrams of the numerical
example 11 of the invention.
FIGS. 20(A), 20(B) and 20(C) are lens block diagrams of the numerical
example 12 of the invention.
FIGS. 21(A), 21(B) and 21(C) are lens block diagrams of the numerical
example 13 of the invention.
FIGS. 22(A), 22(B) and 22(C) are lens block diagrams of the numerical
example 14 of the invention.
FIGS. 23(A)(1)-23(A)(4), 23(B)(1)-23(B)(4), and 23(C)(1)-23(C)(4) are
graphic representations of the aberrations of the numerical example 9.
FIGS. 24(A)(A)(1)-24(A)(4), 24(B)(1)-24(B)(4), and 24(C)(1)-24(C)(4) are
graphic representations of the aberrations of the numerical example 10.
FIGS. 25(A)(1)-25(A)(4), 25(B)(1)-25(B)(4), and 25(C)(1)-25(C)(4) are
graphic representations of the aberrations of the numerical example 11.
FIGS. 26(A)(1)-26(A)(4), 26(B)(1)-26(B)(4), and 26(C)(1)-26(C)(4) are
graphic representations of the aberrations of the numerical example 12.
FIGS. 27(A)(1)-27(A)(4), 27(B)(1)-27(B)(4), and 27(C)(1)-27(C)(4) are
graphic representations of the aberrations of the numerical example 13.
FIGS. 28(A)(1)-28(A)(4), 28(B)(1)-28(B)(1), and 28(C)(1)-20(C)(4) are
graphic representations of the aberrations of the numerical example 14.
FIGS. 29(A), 29(B) and 29(C) are diagrams of the paraxial refractive power
arrangement of the numerical example 15 of the invention.
FIGS. 30(A), 30(B) and 30(C) are diagrams of the paraxial refractive power
arrangement of the numerical example 16 of the invention.
FIGS. 31(A), 31(B) and 31(C) are diagrams of the paraxial refractive power
arrangement of the numerical example 17 of the invention.
FIGS. 32(A), 32(B) and 32(C) are diagrams of the paraxial refractive power
arrangement of the numerical example 18 of the invention.
FIGS. 33(A), 33(B) and 33(C) are diagrams of the paraxial refractive power
arrangement of the numerical example 19 of the invention.
FIGS. 34(A), 34(B) and 34(C) are diagrams of the paraxial refractive power
arrangement of the numerical example 20 of the invention.
FIGS. 35(A), 35(B) and 35(C) are diagrams of the paraxial refractive power
arrangement of the numerical example 21 of the invention.
FIGS. 36(A), 36(B) and 36(C) are diagrams of the paraxial refractive power
arrangement of the numerical example 22 of the invention.
FIGS. 37(A), 37(B) and 37(C) are diagrams of the paraxial refractive power
arrangement of the numerical example 23 of the invention.
FIGS. 38(A), 38(B) and 38(C) are diagrams of the paraxial refractive power
arrangement of the numerical example 24 of the invention.
FIGS. 39(A), 39(B) and 39(C) are diagrams of the paraxial refractive power
arrangement of the numerical example 25 of the invention.
FIGS. 40(A), 40(B) and 40(C) are diagrams of the paraxial refractive power
arrangement of the numerical example 26 of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to an embodiment of the present invention, to reduce the outer
diameter of the zoom lens and also to shorten the physical length thereof,
the following constructions (i) or (ii), or both of them, are, employed.
(i) A zoom lens comprises, from front to rear, a first lens unit of
negative refractive power, a second lens unit of positive refractive power
and a third lens unit of negative refractive power, wherein, when these
three lens units are moved to effect zooming from a wide-angle end to a
telephoto end, at least both the second and third lens units are moved
forward, and at least one of the following conditions is satisfied,
thereby reducing the outer diameter of the lens and obtaining good optical
performance:
##EQU2##
where f.sub.W : the overall focal length in the wide-angle end of the
entire lens system;
f.sub.T : the overall focal length in the telephoto end of the entire lens
system;
f.sub.i : the focal length of the i-th lens unit;
l.sub.1W : the axial air separation between the first lens unit and the
second lens unit in the wide-angle end;
l.sub.2W : the axial air separation between the second lens unit and the
third lens unit in the wide-angle end; and
f.sub.12W : the overall focal length of the first lens unit and the second
lens unit in the wide-angle end.
(ii) A zoom lens comprises, from front to rear, a first lens unit of
negative refractive power, a second lens unit of positive refractive power
and a third lens unit of negative refractive power, wherein, when these
three lens units are moved to effect zooming from a wide-angle end to a
telephoto end, at least both the second and third lens unit are moved
forward, and at least one of the following conditions is satisfied,
thereby minimizing the physical length:
##EQU3##
where e.sub.1W, e.sub.2W, e.sub.1T and e.sub.2T are respectively the
principal point intervals between the first lens unit and the second lens
unit and between the second lens unit and the third lens unit in the
wide-angle end and the telephoto end, f.sub.12W and f.sub.12T are
respectively the overall focal lengths of the first lens unit and the
second lens unit in the wide-angle end and the telephoto end, f.sub.1 and
f.sub.3 are respectively the focal lengths of the first lens unit and the
third lens unit, and f.sub.W and f.sub.T are respectively the focal
lengths of the entire lens system in the wide-angle end and the telephoto
end. It should be noted that the upper limit of the inequalities of
condition (9) may be expanded up to "3.0".
FIGS. 1 to 8 are longitudinal section views of numerical examples 1 to 8 of
an embodiment of the zoom lens according to the invention. In these
figures, I denotes the first lens unit of negative refractive power, II
the second lens unit of positive refractive power and III the third lens
unit of negative refractive power. The arrows show the loci of motion of
the lens units during zooming from the wide-angle end to the telephoto
end. The term "lens unit" used herein should be taken as including one
lens element.
In the zoom lenses of the numerical examples 1 to 8 of this embodiment,
both the second lens unit II and the third lens unit III are made to move
toward the object side. Further, these zoom lenses are made up by
satisfying the above-stated conditions (1) to (6). The technical
significance of each of these conditions (1) to (6) is explained below.
The inequalities of condition (1) are concerned with the focal length of
the first lens unit for the intermediate region of the range of variation
of the focal length (zooming range) of the entire lens system. When the
lower limit is exceeded, as this means that the negative refractive power
of the first lens unit is too strong, the telephoto ratio on the telephoto
side becomes too large, so the total length for the telephoto end of the
entire system comes to increase greatly. When the negative refractive
power of the first lens unit is weak beyond the upper limit, the range of
variation of the separation between the first lens unit and the second
lens unit has to increase in order to obtain a predetermined zoom ratio,
causing the total length of the entire system to become large.
The inequalities of condition (2) are concerned with the refractive power
of the second lens unit. When the lower limit is exceeded, as this means
that the refractive power is too strong, the aberrations vary to a large
extent with zooming. Particularly on the telephoto side, the spherical
aberration becomes difficult to correct well. When the refractive power of
the second lens unit is weak beyond the upper limit, the entire lens
system becomes long in the total length both at the wide-angle and
telephoto ends.
The inequalities of condition (3) are concerned with the refractive power
of the third lens unit. When the refractive power is strong beyond the
lower limit, the movement of the third lens unit gives a larger
contribution to the zooming effect. In other words, the characteristic
feature of the plus-minus form of the 2-unit type emerges, so the back
focal distance becomes short and the outer diameter of the third lens unit
increases. When the upper limit is exceeded, the converse feature or the
minus-plus form of the 2-unit type emerges, so the back focal distance
becomes long. Thus, the entire lens tends to be large in the total length.
The inequalities of condition (4) are concerned with the axial air
separation between the first lens unit and the second lens unit in the
wide-angle end. When the lower limit is exceeded, as this means that the
separation between the first lens unit and the second lens unit is too
short, the zooming effect of the second lens unit becomes so small as to
intensify the tendency to the plus-minus form of the 2-unit type. Thus,
the back focal distance becomes short and the outer diameter of the third
lens unit increases. When the upper limit is exceeded, the outer diameter
of the first lens unit becomes large in a case where a stop is disposed
within the second lens unit.
The inequalities of condition (5) are concerned with the axial air
separation between the second lens unit and the third lens unit in the
wide-angle end. When the air separation between the second lens unit and
the third lens unit is small beyond the lower limit, the result approaches
the minus-plus form of the 2-unit zoom type, so the back focal distance
becomes long. Thus, the entire lens systems tends to become long in the
total length. When the separation between the second lens unit and the
third lens unit is long beyond the upper limit, the back focal distance
becomes short and the outer diameter of the third lens unit increases
largely.
The inequalities of condition (6) are concerned with the ratio of the
overall focal length of the first lens unit and second lens unit in the
wide-angle end to the shortest focal length of the entire system. When the
lower limit is exceeded, the back focal distance becomes short and the
outer diameter of the third lens unit increases greatly. When the upper
limit is exceeded, the total length tends to become long.
Besides these, in the invention it is recommended to set forth the form and
the construction and arrangement of the lens elements as follows: The
first lens unit comprises, from front to rear, at least one negative lens
having a concave surface facing the image side and at least one positive
lens having a convex surface facing the object side. The second lens unit
includes at least two lens surfaces having convex surfaces facing the
object side and at least one lens surface having a convex surface facing
the image side. Again, the frontmost lens in the second lens unit is a
positive lens. The third lens unit includes at least one lens surface
having a concave surface facing the object side.
Next, the technical significances of the above-stated conditions (7), (8)
and (9) are explained.
The inequalities of condition (7) are concerned with the ratio of the
refractive powers of the first lens unit and the third lens unit. When the
lower limit is exceeded, as this means that the refractive power of the
third lens unit is too strong, the back focal distance becomes short and
the outer diameter of the third lens unit increases greatly. When the
upper limit is exceeded, the entire lens tends to become long in the total
length.
The inequalities of condition (8) are concerned with the ratio of the
ranges of variation of the separations between the successive two of the
lens units. When the upper limit is exceeded, the range of variation of
the separation between the second lens unit and the third lens unit
becomes small, while the range of variation of the separation between the
first lens unit and the second lens unit becomes large. Therefore, the
entire lens tends to become long in the total length. As is more
desirable, the upper limit is altered to "6.0". When the lower limit is
exceeded, although this is advantageous for minimizing the size, the total
zooming movement of the third lens unit becomes long and the variation of
the aberrations with zooming becomes difficult to correct.
The inequalities of condition (9) are concerned with the ratio of the
variation of the overall focal length of the first lens unit and the
second lens unit to the variation of the focal length of the entire lens
system. When the lower limit is exceeded, the zooming effect of the second
lens unit becomes weak. Conversely, the refractive power of the third lens
unit becomes strong for zooming purpose and the total zooming movement
becomes long, causing it difficult to correct the variation of the
aberrations with zooming. When the upper limit is exceeded, the zooming
effect of the second lens unit becomes strong and the total length of the
entire lens becomes long.
It is to be noted in the invention that the focusing provision may be made
in the first lens unit as has commonly been used in the prior art, but any
of the rear focus methods such as that known in Japanese Laid-Open Patent
Application No. Sho 64-74521 can be used as well.
Next, numerical examples 1 to 8 of the invention are shown. In the
numerical data for these examples 1 to 8, Ri is the radius of curvature of
the i-th lens surface when counted from the object side; Di is the i-th
lens thickness or air separation when counted from the object side; and Ni
and .nu.i are respectively the refractive index and Abbe number of the
glass of the i-th lens element when counted from the object side.
The values of the factors in the above-stated conditions (1) to (9) for the
numerical examples 1 to 8 are listed in Table-1.
______________________________________
Numerical Example 1
f.sub.W = 39.2
Fno. = 1:4.13-8.26
2.omega. = 57.8.degree.-23.3.degree.
______________________________________
R1 = -141.207
D1 = 1.35 N1 = 1.78590
.nu.1 = 44.2
R2 = 21.077
D2 = 2.53
R3 = 24.944
D3 = 3.20 N2 = 1.80518
.nu.2 = 25.4
R4 = 76.172
D4 = Variable
R5 = 44.548
D5 = 2.70 N3 = 1.48749
.nu.3 = 70.2
R6 = -44.548
D6 = 0.15
R7 = 16.700
D7 = 4.80 N4 = 1.48749
.nu.4 = 70.2
R8 = 76.076
D8 = 0.77
R9 = -59.744
D9 = 5.86 N5 = 1.84666
.nu.5 = 23.9
R10 = 19.546
D10 = 0.44
R11 = 31.964
D11 = 3.46 N6 = 1.69895
.nu.6 = 30.1
R12 = -31.964
D12 = Variable
R13 = -32.895
D13 = 2.50 N7 = 1.74077
.nu.7 = 27.8
R14 = -21.063
D14 = 5.91
R15 = -16.850
D15 = 1.20 N8 = 1.71300
.nu.8 = 53.8
R16 = -17.379
______________________________________
Variable Focal Length
Separation 39.16 50.00 104.74
______________________________________
D4 21.83 14.53 0.80
D12 12.46 11.08 6.64
______________________________________
Numerical Example 2
f.sub.W = 39.1
Fno. = 1:4.14-8.26
2.omega. = 57.9.degree.-23.3.degree.
______________________________________
R1 = -139.371
D1 = 1.35 N1 = 1.79952
.nu.1 = 4.22
R2 = 21.524
D2 = 2.47
R3 = 25.407
D3 = 3.20 N2 = 1.80518
.nu.2 = 25.4
R4 = 81.567
D4 = Variable
R5 = 46.286
D5 = 2.70 N3 = 1.48749
.nu.3 = 70.2
R6 = -46.286
D6 = 0.15
R7 = 16.812
D7 = 4.75 N4 = 1.51633
.nu.4 = 64.2
R8 = 72.069
D8 = 0.76
R9 = -64.911
D9 = 5.90 N5 = 1.84666
.nu.5 = 23.9
R10 = 19.241
D10 = 0.48
R11 = 32.267
D11 = 3.54 N6 = 1.69895
.nu.6 = 30.1
R12 = -32.267
D12 = Variable
R13 = -33.112
D13 = 2.50 N7 = 1.69895
.nu.7 = 30.1
R14 = -20.889
D14 = 5.95
R15 = -16.995
D15 = 1.20 N8 = 1.71300
.nu.8 = 53.8
R16 = -72.147
______________________________________
Variable Focal Length
Separation 39.15 50.00 104.75
______________________________________
D4 21.80 14.51 0.80
D12 12.16 10.77 6.35
______________________________________
Numerical Example 3
f.sub.W = 39.1
Fno. = 1:4.1-8.26
2.omega. = 57.9.degree.-23.3.degree.
______________________________________
R1 = -159.966
D1 = 1.30 N1 = 1.78590
.nu.1 = 44.2
R2 = 20.336
D2 = 2.35
R3 = 23.700
D3 = 3.20 N2 = 1.80518
.nu.2 = 25.4
R4 = 64.799
D4 = Variable
R5 = 24.353
D5 = 3.40 N3 = 1.48749
.nu.3 = 70.2
R6 = -57.202
D6 = 0.15
R7 = 17.397
D7 = 2.50 N4 = 1.51633
.nu.4 = 64.2
R8 = 72.203
D8 = 0.70
R9 = -77.604
D9 = 5.87 N5 = 1.84666
.nu.5 = 23.9
R10 = 17.779
D10 = 0.68
R11 = 38.717
D11 = 5.11 N6 = 1.76182
.nu.6 = 26.5
R12 = -38.717
D12 = Variable
R13 = -37.892
D13 = 2.50 N7 = 1.62004
.nu.7 = 36.3
R14 = -23.128
D14 = 7.13
R15 = -18.594
D15 = 1.25 N8 = 1.71300
.nu.8 = 53.8
R16 = -83.629
______________________________________
Variable Focal Length
Separation 39.15 50.01 104.75
______________________________________
D4 20.09 13.07 0.80
D12 11.21 10.43 5.85
______________________________________
Numerical Example 4
f.sub.W = 39.1
Fno. = 1:4.14-8.26
2.omega. = 57.9.degree.-23.4.degree.
______________________________________
R1 = -137.670
D1 = 1.35 N1 = 1.79952
.nu.1 = 42.2
R2 = 22.270
D2 = 2.78
R3 = 26.333
D3 = 3.20 N2 = 1.80518
.nu.2 = 25.4
R4 = 79.737
D4 = Variable
R5 = 30.649
D5 = 2.80 N3 = 1.51633
.nu.3 = 64.2
R6 = -62.659
D6 = 0.15
R7 = 19.637
D7 = 3.80 N4 = 1.51633
.nu.4 = 64.2
R8 = 151.584
D8 = 0.65
R9 = -59.244
D9 = 6.50 N5 = 1.80518
.nu.5 = 25.4
R10 = 20.064
D10 = 0.53
R11 = 36.108
D11 = 3.69 N6 = 1.68893
.nu.6 = 31.1
R12 = -36.108
D12 = Variable
R13 = -59.123
D13 = 2.50 N7 = 1.51633
.nu.7 = 64.2
R14 = -21.628
D14 = 5.29
R15 = -16.174
D15 = 1.10 N8 = 1.71300
.nu.8 = 53.8
R16 = 59.696
D16 = 2.70 N9 = 1.66680
.nu.9 = 33.0
R17 = -87.613
______________________________________
Variable Focal Length
Separation 39.13 50.00 104.75
______________________________________
D4 22.49 14.28 0.80
D12 10.27 10.18 6.52
______________________________________
Numerical Example 5
f.sub.W = 39.1
Fno. = 1:4.1-8.26
2.omega. = 57.9.degree.-23.4.degree.
______________________________________
R1 = -97.492
D1 = 1.40 N1 = 1.77250
.nu.1 = 49.6
R2 = 21.817
D2 = 2.46
R3 = 25.643
D3 = 3.50 N2 = 1.69895
.nu.2 = 30.1
R4 = 129.338
D4 = Variable
R5 = 44.270
D5 = 2.80 N3 = 1.51633
.nu.3 = 64.2
R6 = -44.270
D6 = 0.15
R7 = 16.584
D7 = 3.86 N4 = 1.51823
.nu.4 = 59.0
R8 = 107.728
D8 = 0.58
R9 = -75.058
D9 = 7.02 N5 = 1.84666
.nu.5 = 23.9
R10 = 18.796
D10 = 0.56
R11 = 37.364
D11 = 3.00 N6 = 1.69895
.nu.6 = 30.1
R12 = -37.364
D12 = Variable
R13 = -40.954
D13 = 2.50 N7 = 1.66680
.nu.7 = 33.0
R14 = -19.368
D14 = 4.52
R15 = -15.498
D15 = 1.40 N8 = 1.69680
.nu.8 = 55.5
R16 = -116.729
______________________________________
Variable Focal Length
Separation 39.14 56.67 104.54
______________________________________
D4 22.02 11.18 0.85
D12 9.29 8.13 4.77
______________________________________
Numerical Example 6
f.sub.W = 39.0
Fno. = 1:4.1-8.27
2.omega. = 58.degree.-23.3.degree.
______________________________________
R1 = -103.674
D1 = 1.40 N1 = 1.74320
.nu.1 = 49.3
R2 = 20.567
D2 = 2.61
R3 = 24.451
D3 = 3.60 N2 = 1.69895
.nu.2 = 30.1
R4 = 103.654
D4 = Variable
R5 = 42.474
D5 = 3.00 N3 = 1.51633
.nu.3 = 64.2
R6 = -42.474
D6 = 0.30
R7 = 17.057
D7 = 3.85 N4 = 1.51633
.nu.4 = 64.2
R8 = 58.696
D8 = 0.85
R9 = -62.761
D9 = 6.80 N5 = 1.84666
.nu.5 = 23.9
R10 = 19.768
D10 = 0.46
R11 = 33.572
D11 = 3.00 N6 = 1.69895
.nu.6 = 30.1
R12 = -33.572
D12 = Variable
R13 = -57.073
D13 = 2.50 N7 = 1.60342
.nu.7 = 38.0
R14 = -20.411
D14 = 4.28
R15 = -16.114
D15 = 1.10 N8 = 1.60311
.nu.8 = 60.7
R16 = 376.813
______________________________________
Variable Focal Length
Separation 39.00 56.32 104.82
______________________________________
D4 22.09 11.69 0.84
D12 10.06 8.00 4.47
______________________________________
Numerical Example 7
f.sub.W = 36.0
Fno. = 1:3.95-8.26
2.omega. = 62.degree.-24.degree.
______________________________________
R1 = -118.409
D1 = 1.30 N1 = 1.80610
.nu.1 = 41.0
R2 = 22.211
D2 = 2.19
R3 = 24.158
D3 = 4.00 N2 = 1.74077
.nu.2 = 27.8
R4 = 87.982
D4 = Variable
R5 = 34.227
D5 = 3.00 N3 = 1.51633
.nu.3 = 64.2
R6 = -59.768
D6 = 1.70
R7 = 17.949
D7 = 4.00 N4 = 1.51742
.nu.4 = 52.4
R8 = -501.981
D8 = 1.41
R9 = -43.400
D9 = 5.00 N5 = 1.84666
.nu.5 = 23.9
R10 = 28.338
D10 = 0.62
R11 = 173.359
D11 = 3.00 N6 = 1.69895
.nu.6 = 30.1
R12 = -32.551
D12 = Variable
R13 = 771.944
D13 = 3.50 N7 = 1.68893
.nu.7 = 31.1
R14 = -35.790
D14 = 4.39
R15 = -15.346
D15 = 1.40 N8 = 1.71300
.nu.8 = 53.8
R16 = -138.628
______________________________________
Variable Focal Length
Separation 36.04 54.55 101.81
______________________________________
D6 23.20 12.20 1.20
D14 13.23 9.92 6.92
______________________________________
Numerical Example 8
f = 39.1-104.7
Fno. = 1:4.1-8.26
2.omega. = 57.9.degree.-23.3.degree.
______________________________________
R1 = -171.489
D1 = 1.30 N1 = 1.78590
.nu.1 = 44.2
R2 = 20.726
D2 = 2.71
R3 = 24.590
D3 = 3.20 N2 = 1.80518
.nu.2 = 25.4
R4 = 68.864
D4 = Variable
R5 = 46.910
D5 = 2.70 N3 = 1.48749
.nu.3 = 70.2
R6 = -47.708
D6 = 0.15
R7 = 16.847
D7 = 5.27 N4 = 1.51633
.nu.4 = 64.2
R8 = 74.377
D8 = 0.78
R9 = -62.237
D9 = 5.19 N5 = 1.84666
.nu.5 = 23.9
R10 = 19.121
D10 = 0.46
R11 = 31.255
D11 = 3.20 N6 = 1.68893
.nu.6 = 31.1
R12 = -31.255
D12 = Variable
R13 = -34.517
D13 = 2.50 N7 = 1.74077
.nu.7 = 27.8
R14 = -21.169
D14 = 5.31
R15 = -16.837
D15 = 1.25 N8 = 1.71300
.nu.8 = 53.8
R16 = -73.193
______________________________________
Variable Focal Length
Separation 39.14 49.97 104.74
______________________________________
D4 21.04 13.81 0.79
D12 13.83 12.54 7.13
______________________________________
TABLE 1
__________________________________________________________________________
Numerical Examples
Conditions 1 2 3 4 5 6 7 8
__________________________________________________________________________
##STR1## 0.823
0.824
0.781
0.820
0.808
0.813
0.869
0.813
##STR2## 0.470
0.468
0.458
0.460
0.455
0.465
0.498
0.469
##STR3## 0.931
0.922
0.922
0.830
0.894
0.922
0.949
0.959
##STR4## 0.557
0.557
0.513
0.575
0.563
0.566
0.644
0.537
##STR5## 0.318
0.311
0.286
0.262
0.237
0.258
0.367
0.353
##STR6## 0.770
0.768
0.779
0.734
0.736
0.748
0.840
0.781
(7) .vertline.f.sub.3 .vertline./.vertline.f.sub.1 .vertline.
1.13
1.12
1.18
1.01
1.11
1.13
1.09
1.18
##STR7## 3.61
3.61
3.60
5.78
4.69
3.80
3.48
3.02
##STR8## 1.02
1.02
1.02
1.02
1.03
1.02
1.02
1.01
__________________________________________________________________________
Another embodiment is next described wherein the image angle is widened.
A wide-angle zoom lens comprises, from front to rear, a first lens unit of
negative refractive power, a second lens unit of positive refractive power
and a third lens unit of negative refractive power, the separations
between these lens units being all varied to effect zooming, wherein,
letting the focal length of the first lens unit be denoted by f.sub.1, the
shortest and longest focal lengths of the entire system by f.sub.W and
f.sub.T respectively, and the diagonal length of the effective area of the
image frame by Y, the following conditions are satisfied:
##EQU4##
FIGS. 17(A), 17(B) and 17(C) to FIGS. 22(A), 22(B) and 22(C) are
longitudinal section views of numerical examples 9 to 14 of zoom lenses to
be described later. FIGS. 23(A)(1)-23(A)(4), 23(B)(1)-23(B)(4) and
23(C)(1)-23(C)(4) are aberration curves of the numerical example 9 in the
wide-angle end, at a medium angle and in the telephoto end. FIGS.
24(A)(1)-24(A)(4), 24(B)(1)-24(B)(4) and 24(C)(1)-24(C)(4) are aberration
curves of the numerical example 10 in the wide-angle end, at a medium
angle and in the telephoto end. FIGS. 25(A)(1)-25(A)(4), 25(B)(1)-25(B)(4)
and 25(C)(1)-25(C)(4) are aberration curves of the numerical example 11 in
the wide-angle end, at a medium angle and in the telephoto end. FIGS.
26(A)(1)-26(A)(4), 26(B)(1)-26(B)(4) and 26(C)(1)-26(C)(4) are aberration
curves of the numerical example 12 in the wide-angle end, at a medium
angle and in the telephoto end. FIGS. 27(A)(1)-27(A)(4), 27(B)(1)-27(B)(4)
and 27(C)(1)-27(C)(4) are aberration curves of the numerical example 13 in
the wide-angle end, at a medium angle and in the telephoto end. FIGS.
28(A), 28(B) and 28(C) are aberration curves of the numerical example 14
in the wide-angle end, at a medium angle and in the telephoto end.
Of the lens block diagrams of FIGS. 17(A), 17(B) and 17(C) to FIGS. 22(A),
22(B) and 22(C), the ones of FIGS. 17(A), 18(A), 19(A), 20(A), 21(A) and
22(A) are in the wide-angle end, the ones of FIGS. 17(B), 18(B), 19(B),
20(B), 21(B) and 22(B) are at the medium angle, and the ones of FIGS.
17(C), 18(C), 19(C), 20(C), 21(C) and 22(C) are in the telephoto end. In
these figures, L1 denotes the first lens unit of negative refractive
power; L2 the second lens unit of positive refractive power; and L3 the
third lens unit of negative refractive power. SP stands for the aperture
stop, and FP for the image plane.
In this embodiment, zooming from the wide-angle end to the telephoto end is
performed in such a manner that, the first lens unit moves axially while
depicting a locus convex toward the image side and both the second lens
unit and the third lens unit move axially forward, as indicated by the
arrows, while depicting linear or non-linear loci, so that the air
separation between the first lens unit and the second lens unit decreases
and the air separation between the second lens unit and the third lens
unit decreases.
Within this framework, the above-stated conditions (10) and (11) are
considered when designing each lens unit. Thus, the requirements of
shortening the total length of the entire lens with the zoom ratio kept at
a predetermined value and of increasing the maximum image angle to
90.degree. or thereabout are simultaneously fulfilled.
Incidentally, focusing is performed by moving the first lens unit.
The technical significance of each of the above-stated conditions (10) and
(11) is explained below.
The inequalities of condition (10) are concerned with the ratio of the
focal length of the first lens unit to the focal length of the entire
system at a medium angle in the range of variation of the focal length (or
at the medium zooming position), and have an aim chiefly to maintain good
optical performance over the entire zooming range, while still permitting
the shortening of the total length of the entire lens to be achieved.
When the lower limit of the condition (10) is exceeded, as this means that
the negative refractive power of the first lens unit is too strong, the
telephoto ratio for the telephoto side becomes large, causing the total
length of the entire lens to increase on the telephoto side and also
causing the variation with zooming of the aberrations to increase greatly.
When the negative refractive power of the first lens unit is weak beyond
the upper limit, the aberrations are easy to correct, but the required
amount of movement for the predetermined zoom ratio of the first lens unit
becomes large, causing the total length of the entire lens to increase
objectionably.
The inequalities of condition (11) are concerned with the ratio of the
focal length of the entire system at the medium angle in the range of
variation of the focal length (at the medium zooming position) to the
image size, or the angle of field of view, and have an aim chiefly to
increase the maximum image angle with the zoom ratio kept at the
predetermined value.
When the lower limit of the condition (11) is exceeded, as this means that
the focal length for the telephoto side is too short, the predetermined
zoom ratio becomes difficult to realize. When the focal length for the
telephoto side is too long, as exceeding the upper limit, the separation
for the wide-angle end between the first lens unit and the second lens
unit becomes wide. To increase the maximum image angle, therefore, the
diameter of the front lens element increases objectionably.
In this embodiment, to increase the maximum image angle to 90.degree. or
more and obtain good optical performance throughout the entire zooming
range, it is preferred to satisfy the following conditions:
0.4<.vertline.f.sub.1 .vertline./Y<0.7 (12)
0.2<.vertline.f.sub.2 /f.sub.3 .vertline.<0.8 (13)
where f.sub.2 and f.sub.3 are the focal lengths of the second lens unit and
the third lens unit, respectively.
The inequalities of condition (12) are concerned with the ratio of the
focal length of the first lens unit to the image size, and have an aim
chiefly to shorten the total length of the entire lens with the
maintenance of the predetermined zoom ratio.
When the negative refractive power of the first lens unit is too strong as
exceeding the lower limit of the condition (12), the total length for the
telephoto side of the entire lens becomes long. When the negative
refractive power of the first lens unit is too weak as exceeding the upper
limit, the maximum image angle becomes difficult to increase under the
condition that the predetermined zoom ratio is secured.
The inequalities of condition (13) are concerned with the ratio of the
focal lengths of the second lens unit and the third lens unit, and have an
aim chiefly to secure the predetermined back focal distance and zoom
ratio.
When the negative refractive power of the third lens unit is too weak as
exceeding the lower limit of the condition (13), the telephoto type comes
to collapse, making it difficult to shorten the total length of the entire
lens with the zoom ratio secured at the predetermined value. When the
negative refractive power of the third lens unit is too strong as
exceeding the upper limit, the back focal distance for the wide-angle end
becomes short and the diameter of the rear lens element increases
objectionably.
It is to be noted in the present embodiment that the optical performance is
maintained in good balance over the entire area of the image frame when
the stop is positioned within the second lens unit, and asphere is applied
to at least one lens surface on the object side of the stop.
Also, in the present embodiment, zooming may be otherwise performed by
moving the second lens unit and the third lens unit non-linearly, while
the first lens unit remains stationary. Focusing may be otherwise
performed by moving either the second lens unit or the third lens unit.
In the zoom lens in the present embodiment, the first lens unit for the
numerical examples 9, 11, 12 and 14 is constructed from three lenses,
i.e., a meniscus-shaped negative lens having a convex surface facing the
object side, a negative lens and a meniscus-shaped positive lens having a
convex surface facing the object side. For the numerical examples 10 and
13, the first lens unit is constructed from two lenses, i.e., a
meniscus-shaped negative lens having a convex surface facing the object
side and a meniscus-shaped positive lens having a convex surface facing
the object side.
Again, in the numerical example 10, the rear surface of the positive lens
in the first lens unit is made aspherical.
The second lens unit for the numerical examples 9, 10, 11, 13 and 14 is
constructed from six lenses, i.e., a positive lens whose surfaces both are
convex and having a strong refracting surface facing the image side, a
cemented lens composed of a positive lens and a negative lens, a cemented
lens composed of a positive lens and a negative lens, and a positive lens.
For the numerical example 12, the second lens unit is constructed from five
lenses, i.e., a positive lens, a cemented lens composed of a positive lens
and a negative lens, a negative lens and a positive lens.
The third lens unit for the numerical examples 9 to 14 is constructed from
two lenses, i.e., a positive lens and a negative lens having a strong
negative refracting surface facing the object side.
Next, the numerical data for the examples 9 to 14 are shown, where Ri is
the radius of curvature of the i-th lens surface when counted from the
object side; Di is the i-th lens thickness or air separation when counted
from the object side; and Ni and .nu.i are respectively the refractive
index and Abbe number of the glass of the i-th lens element when counted
from the object side.
The values of the factors in the above-stated conditions (10) to (13) for
the numerical examples 9 to 14 are listed in Table-2.
The aspherical shape is expressed in the ordinates with an X axis in the
axial direction and an H axis in the direction perpendicular to the
optical axis, the direction in which light advances being taken as
positive, by the following equation:
##EQU5##
where R is the radius of the osculating sphere, and A, B, C, D and E are
the aspheric coefficients.
______________________________________
Numerical Example 9
f = 21.3-29.5
Fno. = 1:3.6-4.6 2.omega. = 91.2.degree.-72.4.degree.
______________________________________
R1 = 69.48
D1 = 1.30 N1 = 1.83400
.nu.1 = 37.2
R2 = 14.49
D2 = 4.45
R3 = -1660.67
D3 = 1.20 N2 = 1.58313
.nu.2 = 59.4
R4 = 33.96
D4 = 1.72
R5 = 19.42
D5 = 2.50 N3 = 1.80518
.nu.3 = 25.4
R6 = 42.54
D6 = Variable
R7 = 56.58
D7 = 2.20 N4 = 1.60738
.nu.4 = 56.8
R8 = -33.38
D8 = 1.24
R9 = (Stop)
D9 = 0.46
R10 = 17.88
D10 = 4.60 N5 = 1.63930
.nu.5 = 44.9
R11 = -13.01
D11 = 2.10 N6 = 1.80610
.nu.6 = 41.0
R12 = 53.04
D12 = 0.25
R13 = 26.08
D13 = 3.30 N7 = 1.69680
.nu.7 = 55.5
R14 = -22.28
D14 = 1.00 N8 = 1.80518
.nu.8 = 25.4
R15 = 16.65
D15 = 1.15
R16 = 215.06
D16 = 2.10 N9 = 1.66680
.nu.9 = 33.0
R17 = -16.91
D17 = Variable
R18 = -41.97
D18 = 2.20 N10 = 1.69895
.nu.10 = 30.1
R19 = -24.59
D19 = 3.59
R20 = -13.08
D20 = 1.00 N11 = 1.71300
.nu.11 = 53.8
R21 = -35.54
______________________________________
Variable Focal Length
Separation 21.30 25.55 29.50
______________________________________
D6 7.56 4.54 2.63
D17 11.31 10.01 8.71
______________________________________
R4: Aspheric
A = 0 D = 2.49 .times. 10.sup.-9
B = -2.38 .times. 10.sup.-6
E = -9.68 .times. 10.sup.-12
C = -1.83 .times. 10.sup.-7
______________________________________
Numerical Example 10
f = 21.4-29.6
Fno. = 1:3.6-4.6 2.omega. = 91.2.degree.-72.4.degree.
______________________________________
R1 = 136.29
D1 = 1.64 N1 = 1.80400
.nu.1 = 46.6
R2 = 12.62
D2 = 5.95
R3 = 18.86
D3 = 3.28 N2 = 1.78472
.nu.2 = 25.7
R4 = 29.62
D4 = Variable
R5 = 88.19
D5 = 2.90 N3 = 1.58313
.nu.3 = 59.4
R6 = -24.77
D6 = 0.25
R7 = 18.49
D7 = 5.04 N4 = 1.63930
.nu.4 = 44.9
R8 = -13.46
D8 = 1.89 N5 = 1.80610
.nu.5 = 41.0
R9 = 36.27
D9 = 1.39
R10 = 20.69
D10 = 1.13
(Stop)
R11 = 20.80
D11 = 3.32 N6 = 1.62299
.nu.6 = 58.2
R12 = -19.82
D12 = 1.26 N7 = 1.80518
.nu.7 = 25.4
R13 = 19.92
D13 = 1.01
R14 = 111.24
D14 = 2.90 N8 = 1.64769
.nu.8 = 33.8
R15 = -17.72
D15 = Variable
R16 = 130.36
D16 = 3.15 N9 = 1.80518
.nu.9 = 25.4
R17 = -55.73
D17 = 4.05
R18 = -13.96
D18 = 1.51 N10 = 1.77250
.nu.10 = 49.6
R19 = -81.13
______________________________________
Variable Focal Length
Separation 21.17 25.44 29.58
______________________________________
D4 8.09 4.80 2.57
D15 6.12 5.38 4.63
______________________________________
R4: Aspheric
A = 0 D= -2.33 .times. 10.sup.-10
B = -9.67 .times. 10.sup.-6
E = 2.92 .times. 10.sup.-14
C = -6.17 .times. 10.sup.-8
______________________________________
Numerical Example 11
f = 21.4-29.5
Fno. = 1:3.6-4.6 2.omega. = 90.6.degree.-72.4.degree.
______________________________________
R1 = 359.46
D1 = 1.39 N1 = 1.83400
.nu.1 = 37.2
R2 = 14.53
D2 = 3.25
R3 = 48.81
D3 = 1.26 N2 = 1.69680
.nu.2 = 55.5
R4 = 20.87
D4 = 1.89
R5 = 19.17
D5 = 3.78 N3 = 1.80518
.nu.3 = 25.4
R6 = 63.71
D6 = Variable
R7 = 50.13
D7 = 3.40 N4 = 1.51633
.nu.4 = 64.2
R8 = -24.69
D8 = 0.25
R9 = 15.73
D9 = 4.16 N5 = 1.58313
.nu.5 = 59.4
R10 = -18.99
D10 = 1.13 N6 = 1.80610
.nu.6 = 41.0
R11 = 70.65
D11 = 1.89
R12 = (Stop)
D12 = 1.26
R13 = 29.68
D13 = 2.27 N7 = 1.51633
.nu.7 = 64.2
R14 = -27.29
D14 = 1.26 N8 = 1.80518
.nu.8 = 25.4
R15 = 22.30
D15 = 1.01
R16 = 75.19
D16 = 3.15 N9 = 1.66680
.nu.9 = 33.0
R17 = -18.70
D17 = Variable
R18 = 262.09
D18 = 2.52 N10 = 1.64769
.nu.10 = 33.8
R19 = -39.83
D19 = 3.87
R20 = -10.44
D20 = 1.51 N11 = 1.71300
.nu.11 = 53.8
R21 = -59.56
______________________________________
Variable Focal Length
Separation 21.42 25.50 29.48
______________________________________
D6 7.07 4.21 2.21
D17 3.40 3.08 2.75
______________________________________
R9: Aspheric
A = 0 D = 9.07 .times. 10.sup.-10
B = -3.64 .times. 10.sup.-6
E = 0
C = -3.08 .times. 10.sup.-7
______________________________________
Numerical Example 12
f = 21.4-29.5
Fno. = 1:3.6-4.6 2.omega. = 90.6.degree.-72.4.degree.
______________________________________
R1 = 462.84
D1 = 1.39 N1 = 1.83400
.nu.1 = 37.2
R2 = 16.56
D2 = 3.36
R3 = 46.27
D3 = 1.26 N2 = 1.69680
.nu.2 = 55.5
R4 = 20.33
D4 = 1.88
R5 = 20.44
D5 = 4.03 N3 = 1.80518
.nu.3 = 25.4
R6 = 76.19
D6 = Variable
R7 = -2143.42
D7 = 3.78 N4 = 1.51633
.nu.4 = 64.2
R8 = -27.09
D8 = 0.25
R9 = 18.30
D9 = 5.29 N5 = 1.58313
.nu.5 = 59.4
R10 = -22.63
D10 = 1.13 N6 = 1.80518
.nu.6 = 25.4
R11 = -91.98
D11 = 2.02
R12 = (Stop)
D12 = 2.90
R13 = 88.01
D13 = 1.26 N7 = 1.80518
.nu.7 = 25.4
R14 = 19.53
D14 = 1.01
R15 = 84.29
D15 = 2.90 N8 = 1.63930
.nu.8 = 44.9
R16 = -20.06
D16 = Variable
R17 = -47.55
D17 = 2.52 N9 = 1.64769
.nu.9 = 33.8
R18 = -22.68
D18 = 3.39
R19 = -12.03
D19 = 1.51 N10 = 1.71300
.nu.10 = 53.8
R20 = -51.94
______________________________________
Variable Focal Length
Separation 21.42 25.52 29.48
______________________________________
D6 8.60 4.99 2.50
D16 6.05 5.57 5.08
______________________________________
R9: Aspheric
A = 0 D = 7.04 .times. 10.sup.-10
B = -1.82 .times. 10.sup.-5
E = 0
C = -2.14 .times. 10.sup.-7
______________________________________
Numerical Example 13
f = 21.4-29.5
Fno. = 1:3.6-4.6 2.omega. = 90.6.degree.-72.4.degree.
______________________________________
R1 = 181.65
D1 = 1.64 N1 = 1.80400
.nu.1 = 46.6
R2 = 13.07
D2 = 5.82
R3 = 16.81
D3 = 3.28 N2 = 1.80518
.nu.2 = 25.4
R4 = 23.28
D4 = Variable
R5 = 63.88
D5 = 3.15 N3 = 1.58313
.nu.3 = 59.4
R6 = -23.56
D6 = 0.25
R7 = 18.49
D7 = 5.04 N4 = 1.63930
.nu.4 = 44.9
R8 = -12.55
D8 = 1.89 N5 = 1.80610
.nu.5 = 41.0
R9 = 28.91
D9 = 1.39
R10 = 20.69
D10 = 1.13
(Stop)
R11 = 21.37
D11 = 3.32 N6 = 1.69680
.nu.6 = 55.5
R12 = -26.39
D12 = 1.26 N7 = 1.80518
.nu.7 = 25.4
R13 = 18.26
D13 = 1.01
R14 = 227.69
D14 = 2.77 N8 = 1.66680
.nu.8 = 33.0
R15 = -17.94
D15 = Variable
R16 = 126.60
D16 = 3.15 N9 = 1.68893
.nu.9 = 31.1
R17 = -47.91
D17 = 3.49
R18 = -17.61
D18 = 1.51 N10 = 1.71300
.nu.10 = 53.8
R19 = -449.15
______________________________________
Variable Focal Length
Separation 21.42 25.51 29.48
D4 7.55 4.53 2.43
D15 8.21 7.39 6.57
______________________________________
R5: Aspheric
A = 0 D = -9.73 .times. 10.sup.-10
B = -1.1 .times. 10.sup.-6
E = 0
C = 1.24 .times. 10.sup.-7
______________________________________
Numerical Example 14
f = 24.9-34.0
Fno. = 1:3.6-4.6 2.omega. = 82.0.degree.-72.4.degree.
______________________________________
R1 = 71.73
D1 = 1.24 N1 = 1.83400
.nu.1 = 37.2
R2 = 14.23
D2 = 3.76
R3 = -199.96
D3 = 1.02 N2 = 1.58313
.nu.2 = 59.4
R4 = 48.96
D4 = 1.76
R5 = 19.67
D5 = 2.84 N3 = 1.80518
.nu.3 = 25.4
R6 = 40.89
D6 = Variable
R7 = 52.66
D7 = 1.90 N4 = 1.60738
.nu.4 = 56.8
R8 = -36.42
D8 = 1.24
R9 = (Stop)
D9 = 0.46
R10 = 17.66
D10 = 4.58 N5 = 1.63930
.nu.5 = 44.9
R11 = -12.85
D11 = 2.10 N6 = 1.80610
.nu.6 = 41.0
R12 = 52.95
D12 = 0.16
R13 = 25.98
D13 = 3.27 N7 = 1.69680
.nu.7 = 55.5
R14 = -29.01
D14 = 0.85 N8 = 1.80518
.nu.8 = 25.4
R15 = 16.70
D15 = 1.15
R16 = 407.90
D16 = 1.90 N9 = 1.66680
.nu.9 = 33.0
R17 = -17.39
D17 = Variable
R18 = (Flare
D18 = Variable
Stop)
R19 = -33.35
D19 = 1.91 N10 = 1.69895
.nu.10 = 30.1
R20 = -22.48
D20 = 3.14
R21 = -12.96
D21 = 0.92 N11 = 1.71300
.nu.11 = 53.8
R22 = -30.45
______________________________________
Variable Focal Length
Separation 24.90 29.63 34.00
______________________________________
D6 6.65 4.19 2.64
D17 -0.50 2.73 5.95
D18 12.81 8.15 3.48
______________________________________
R4: Aspheric
A = 0 D = 2.15 .times. 10.sup.-9
B = 1.76 .times. 10.sup.-5
E = -8.64 .times. 10.sup.-12
C = -1.57 .times. 10.sup.-7
______________________________________
Flare Stop: a stop for cutting off a bundle of rays causing flare
TABLE 2
______________________________________
Numerical Examples
Conditions 9 10 11 12 13 14
______________________________________
##STR9## 1.09 1.07 1.02 1.17 1.03 0.94
##STR10## 0.58 0.58 0.58 0.58 0.58 0.67
(12) .vertline.f.sub.1 .vertline./Y
0.63 0.62 0.59 0.68 0.60 0.63
(13) .vertline.f.sub.2 /f.sub.3 .vertline.
0.41 0.42 0.62 0.56 0.33 0.39
______________________________________
A further embodiment is next described where the zooming range is extended.
(A) A zoom lens is provided, comprising, from front to rear, a first lens
unit of negative refractive power, a second lens unit of positive
refractive power and a third lens unit of negative refractive power,
wherein two lens units of the first, second and third lens units are made
to axially move in unison to perform a first zooming operation from a
wide-angle end to a medium focal length position and, after that, the two
lens units are isolated from each other and at least one lens unit of the
two lens units is made to axially move to perform a second zooming
operation from the medium focal length position to a telephoto end.
(B) A zoom lens is provided, comprising, from front to rear, a first lens
unit of negative refractive power, a second lens unit of positive
refractive power and a third lens unit of negative refractive power,
wherein as zooming is performed by moving the first, second and third lens
units, two lens units of the first, second and third lens units are made
to axially move in unison to perform a first zooming operation from a
wide-angle end to a medium focal length position and, after that, the two
lens units are isolated from each other and made to move in differential
relation to perform a second zooming operation from the medium focal
length position to a telephoto end.
In particular, the first zooming operation is performed by moving either
the first lens unit and the third lens unit in unison, or the first lens
unit and the second lens unit in unison, or the second lens unit and the
third lens unit in unison, and the first, second and third lens units are
moved all forward when the first zooming operation and the second zooming
operation are carried out.
For the event of transition from the first zooming operation to the second
zooming operation, there are determined the principal point interval e1M
between the first lens unit and the second lens unit, the principal point
interval e2M between the second lens unit and the third lens unit and the
focal length fM of the entire system; and for the telephoto end, there are
determined the principal point interval e1T between the first lens unit
and the second lens unit, the principal point interval e2T between the
second lens unit and the third lens unit and the focal length fT of the
entire system. The zoom lens then satisfies at least one of the following
condition:
-0.5<(e1T-e1M)/(fT-fM)<0.1 (14)
-0.5<(e2T-e2M)/(fT-fM)<0.1 (15)
(C) A zoom lens is provided, comprising, from front to rear, a first lens
unit of negative refractive power, a second lens unit of positive
refractive power, and a third lens unit of negative refractive power,
wherein the first, second and third lens units are moved to perform a
first zooming operation and, after that, at least one lens unit of the
first lens unit and the third lens unit is rendered stationary and the
second lens unit is moved to perform a second zooming operation.
In particular, the first zooming operation is performed by moving the first
lens unit, the second lens unit and the third lens unit all forward, and
the second zooming operation is performed by moving the second lens unit
forward.
Also, letting the focal length of the i-th lens unit be denoted by fi, the
overall focal length for an arbitrary zooming position of the second lens
unit and the third lens unit by f23 and the shortest and longest focal
lengths of the entire system by fW and fT, respectively, the following
conditions are satisfied:
0<fW(1/f1+2/f2+1/f3)<4 (16)
0<f23/fT<0.9 (17)
In addition, for the event of transition from the first zooming operation
to the second zooming operation, there are determined the principal point
interval e1m between the first lens unit and the second lens unit, the
principal point interval e2M between the second lens unit and the third
lens unit and the focal length fM of the entire lens; and for the
telephoto end, there are determined the principal point interval e1T
between the first lens unit and the second lens unit, the principal point
interval e2T between the second lens unit and the third lens unit and the
focal length fT of the entire system. The zoom lens then satisfies at
least one of the following conditions:
-0.5<(e1T-e1M)/(fT-fM)<0.1 (18)
-0.5<(e2T-e2M)/(fT-fM)<0.1 (19)
(D) A zoom lens comprises, from front to rear, a first lens unit of
negative refractive power, a second lens unit of positive refractive power
and a third lens unit of negative refractive power, wherein the second
lens unit is moved and at least one of the first lens unit and the third
lens unit remains stationary to perform a first zooming operation, and,
after that, the first, second and third lens units are moved to perform a
second zooming operation.
In particular, the first lens unit and the second lens unit are moved in
unison and the third lens unit is moved in differential relation, each
forward, to perform the second zooming operation.
Also, letting the focal length of the i-th lens unit be denoted by fi, the
overall focal length for an arbitrary zooming position of the second lens
unit and the third lens unit by f23 and the shortest and longest focal
lengths of the entire system by fW and fT, respectively, the following
conditions are satisfied:
0<fW(1/f1+2/f2+1/f3)<4 (20)
0<f23/fT<0.9 (21)
In addition, for the event of transition from the first zooming operation
to the second zooming operation, there are determined the principal point
interval e1m between the first lens unit and the second lens unit, the
principal point interval e2M between the second lens unit and the third
lens unit and the focal length fM of the entire system; and for the
telephoto end, there are determined the principal point interval e1T
between the first lens unit and the second lens unit, the principal point
interval e2T between the second lens unit and the third lens unit and the
focal length fT of the entire system. The zoom lens then satisfies at
least one of the following conditions:
-0.5<(e1T-e1M)/(fT-fM)<0.1 (22)
-0.5<(e2T-e2M)/(fT-fM)<0.1 (23)
(E) A zoom lens comprises, from front to rear, a first lens unit of
negative refractive power, a second lens unit of positive refractive power
and a third lens unit of positive or negative refractive power, wherein as
zooming is performed by moving the first, second and third lens units, the
first, second and third lens units are moved in differential relation to
perform a first zooming operation from a wide-angle end to a medium focal
length position and, after that, two lens units of the first, second and
third lens units are moved in unison to perform a second zooming operation
from the medium focal length position to a telephoto position.
In particular, the first zooming operation and the second zooming operation
are performed by moving the first, second and third lens units all
forward. The second zooming operation is performed by moving either the
first lens unit and the third lens unit in unison, or the first lens unit
and the second lens unit in unison, or the second lens unit and the third
lens unit in unison.
For the event of transition from the first zooming operation to the second
zooming operation, there are determined the principal point interval e1m
between the first lens unit and the second lens unit, the principal point
interval e2M between the second lens unit and the third lens unit and the
focal length fM of the entire system; and for the telephoto end, there are
determined the principal point interval e1T between the first lens unit
and the second lens unit, the principal point interval e2T between the
second lens unit and the third lens unit and the focal length fT of the
entire system. The zoom lens then satisfies at least one of the following
conditions:
-0.5<(e1T-e1M)/(fT-fM)<0.1 (24)
-0.5<(e2T-e2M)/(fT-fM)<0.1 (25)
FIGS. 29(A), 29(B) and 29(C) to FIGS. 31(A), 31(B) and 31(C) show the
paraxial refractive power arrangements of numerical examples 15 to 17.
In these figures, L1 denotes the first lens unit of negative refractive
power; L2 the second lens unit of positive refractive power; L3 the third
lens unit of positive or negative refractive power; and FP the image
plane. FIGS. 29(A), 30(A) and 31(A) are in the wide-angle end; FIGS.
29(B), 30(B) and 31(B) in a medium zooming position; and FIGS. 29(C),
30(C) and 31(C) in the telephoto end. The arrows indicate the moving
directions of the lens units during zooming.
The numerical examples 15 to 17 each comprise, from front to rear, a first
lens unit of negative refractive power, a second lens unit of positive
refractive power and a third lens unit of negative refractive power,
totaling three lens units, of which two lens units are moved in unison to
perform the first zooming operation from the wide-angle end (A) to the
medium focal length position (B). After that, the two lens units are taken
out of unison and at least one of them is then moved to perform the second
zooming operation from the medium focal length position (B) to the
telephoto end (C).
Concretely speaking, as the three lens units are moved forward to effect
zooming from the wide-angle end to the telephoto end, two of the three
lens units are moved in unison to perform the first zooming operation from
the wide-angle end to the medium focal length position. After that, the
two lens units are taken out of unison and then moved in differential
relation to perform the second zooming operation from the medium focal
length position to the telephoto end.
Especially, the first zooming operation is performed by moving forward the
first lens unit and the third lens unit in unison for the numerical
example 15 of FIGS. 29(A) to 29(C), the first lens unit and the second
lens unit in unison for the numerical example 16 of FIGS. 30(A) to 30(C),
or the second lens unit and the third lens unit in unison for the
numerical example 17 of FIGS. 31(A) to 31(C).
The second zooming operation for each of the numerical examples 15 to 17 is
performed by moving the three lens units forward in differential relation.
In the numerical example 15 of FIGS. 29(A) to 29(C), the differential
relation is such that, during the first zooming operation, the separation
between the first lens unit and the second lens unit decreases and the
separation between the second lens unit and the third lens unit increases
and that during the second zooming operation, the separation between the
first lens unit and the second lens unit decreases and the separation
between the second lens unit and the third lens unit decreases.
In the numerical example 16 of FIGS. 30(A) to 30(C), during the first
zooming operation, the separation between the second lens unit and the
third lens unit decreases. During the second zooming operation, the
separation between the first lens unit and the second lens unit decreases
and the separation between the second lens unit and the third lens unit
increases.
In the numerical example 17 of FIGS. 31(A) to 31(C), during the first
zooming operation, the separation between the first lens unit and the
second lens unit decreases. During the second zooming operation, the
separation between the first lens unit and the second lens unit decreases
and the separation between the second lens unit and the third lens unit
increases.
In the numerical examples 15 to 17, for the medium focal length position
(B) at which to interchange the system between the two zoom types and the
telephoto end (C), all the lens units have paraxial refractive power
arrangements determined with every parameter satisfying at least one of
the conditions (14) and (15).
By this, a predetermined zoom ratio is easy to obtain while still
maintaining the lens mounting mechanism to be simplified in structure.
Moreover, the maximum image angle is easy to widen. Nonetheless, the zoom
lens can be constructed in a compact form.
When the upper limit of the condition (14) or (15) is exceeded, the
separations between the lens units in the region of from the medium focal
length position to the telephoto end become too wide with the result of
increasing the total length of the entire lens objectionably. When the
lower limit is exceeded, the ranges of variation with zooming of the
separations between the lens units become large. Thus, a long lens barrel
is required and the size of the entire system comes to increase greatly.
FIGS. 32(A), 32(B) and 32(C) to FIGS. 34(A), 34(B) and 34(C) show the
paraxial refractive power arrangements of the numerical examples 18 to 20
of the invention.
In these figures, L1 denotes the first lens unit of negative refractive
power; L2 the second lens unit of positive refractive power; L3 the third
lens unit of positive or negative refractive power; and FP the image
plane. FIGS. 32(A), 33(A) and 34(A) are in the wide-angle end; FIGS.
32(B), 33(B) and 34(B) in the medium focal length position; and FIGS.
32(C), 33(C) and 34(C) in the telephoto end. The arrows indicate the
moving directions of the lens units during zooming.
The numerical examples 18 to 20 each comprise, from front to rear, a first
lens unit of negative refractive power, a second lens unit of positive
refractive power and a third lens unit of negative refractive power,
totaling three lens units, all of which are moved forward to perform a
first zooming operation from the wide-angle end (A) to the medium focal
length position (B). After that, at least one of the first lens unit and
the third lens unit is rendered stationary. Then, the second lens unit is
moved forward to perform a second zooming operation from the medium focal
length position (B) to the telephoto end (C).
Especially, the first zooming operation is performed for the numerical
examples 18 and 19 of FIGS. 32(A) to 32(C) and FIGS. 33(A) to 33(C) by
moving the first lens unit, the second lens unit and the third lens unit
forward in differential relation, or for the numerical example 20 of FIGS.
34(A) to 34(C) by moving the second lens unit and the third lens unit
forward in unison.
During the second zooming operation, for the numerical example 18 of FIGS.
32(A) to 33(C), the first lens unit is rendered stationary, and the second
lens unit and the third lens unit move. For the numerical example 19 of
FIGS. 33(A) to 33(C), the third lens unit is rendered stationary, and the
first lens unit and the second lens unit move. For the numerical example
20 of FIGS. 34(A) to 34(C), the first lens unit and the third lens unit
are rendered stationary, and the second lens unit moves.
It should be noted in connection with the numerical example 20 that the
second zooming operation works in only two focal length positions, namely,
the medium and longest focal length positions, and is not used in their
intervening region of the zooming range.
In the numerical example 18 of FIGS. 32(A) to 32(C), the differential
relation is such that, during the first zooming operation, the separation
between the first lens unit and the second lens unit decreases, and the
separation between the second lens unit and the third lens unit decreases.
During the second zooming operation, the separation between the first lens
unit and the second lens unit decreases and the separation between the
second lens unit and the third lens unit increases.
In the numerical example 19 of FIGS. 33(A) to 33(C), during the first
zooming operation, the separation between the first lens unit and the
second lens unit decreases and the separation between the second lens unit
and the third lens unit decreases. During the second zooming operation,
the separation between the first lens unit and the second lens unit
decreases and the separation between the second lens unit and the third
lens unit increases.
In the numerical example 20 of FIGS. 34(A) to 34(C), during the first
zooming operation, the separation between the first lens unit and the
second lens unit decreases. During the second zooming operation, the
separation between the first lens unit and the second lens unit decreases
and the separation between the second lens unit and the third lens unit
increases.
In the numerical examples 18 to 20, the lens units are made up by
determining their refractive powers so as to satisfy the above-stated
conditions (16) and (17). By this, all the aberrations become easy to
correct, while still permitting the entire lens system to be minimized in
size.
When the lower limit of the condition (16) is exceeded, as this means that
the negative refractive powers of the first lens unit and the third lens
unit are too strong, or that the positive refractive power of the second
lens unit comes to be weak, curvature of field becomes over-corrected.
Conversely when the upper limit is exceeded, under-correction of field
curvature results.
The inequalities of condition (17) give a proper range for the overall
positive refractive power of the second lens unit and the third lens unit
and have an aim to make the image good in the angular field coverage
characteristic, while still permitting the total length of the entire lens
to be shortened.
When the upper limit of the condition (17) is exceeded, as this means that
the positive refractive power is too weak, the total length in the
wide-angle end of the entire lens becomes long. When the lower limit is
exceeded, as this means that the overall refractive power of the second
lens unit and the third lens unit changes to the negative, the curvature
of field increases objectionably.
Again, in the numerical examples 18 to 20, similarly to the numerical
examples 15 to 17, for the medium focal length position (B) at which to
interchange the system between the two zoom types and the telephoto end,
all the lens units have paraxial refractive power arrangements determined
with every parameter satisfying at least one of the conditions (18) and
(19).
By this, a predetermined zoom ratio is easily obtained, while still
permitting the lens mounting mechanism to be simplified in structure.
Moreover, the maximum image angle is easy to widen. Nonetheless, the size
of the entire lens system can be minimized.
The technical significances of the conditions (18) and (19) are similar to
those of the above-stated conditions (14) and (15).
FIGS. 35(A), 35(B) and 35(C) to FIGS. 37(A), 37(B) and 37(C) are schematic
diagrams of the paraxial refractive power arrangements of the numerical
examples 21 to 23 of the invention.
In these figures, L1 denotes the first lens unit of negative refractive
power; L2 the second lens unit of positive refractive power; L3 the third
lens unit of positive or negative refractive power; and FP the image
plane. Again, FIGS. 35(A), 36(A) and 37(A) are in the wide-angle end;
FIGS. 35(B), 36(B) and 37(B) are in a medium focal length position; and
FIGS. 35(C), 36(C) and 37(C) are in the telephoto end. The arrows indicate
the moving directions of the lens units during zooming.
The numerical examples 21 to 23 each comprise, from front to rear, a first
lens unit of negative refractive power, a second lens unit of positive
refractive power and a third lens unit of negative refractive power,
totaling three lens units, wherein the second lens unit is moved forward,
and at least one of the first lens unit and the third lens unit is made
stationary to perform a first zooming operation from the wide-angle end
(A) to the medium focal length position (B), and, after that, the three
lens units are moved forward to perform a second zooming operation from
the medium focal length position (B) to the telephoto end (C).
Especially, the first zooming operation is performed by moving forward the
second lens unit and the third lens unit for the numerical example 21 of
FIGS. 35(A) to 35(C), the first lens unit and the second lens unit for the
numerical example 22 of FIGS. 36(A) to 36(C), or only the second lens unit
for the numerical example 23 of FIGS. 37(A) to 37(C).
The second zooming operation is performed for each of the numerical
examples 21 to 23 by moving forward the first lens unit and the second
lens unit in unison and the third lens unit in differential relation.
It should be noted in connection with the numerical example 23 of FIGS.
37((A) to 37(C) that the first zooming operation works at only two focal
length positions, namely, the shortest and medium focal length positions,
and is not used in their intervening region of the zooming range.
In the numerical example 21 of FIGS. 35(A) to 35(C), the differential
relation is such that during the first zooming operation, the first lens
unit remains stationary, the separation between the first lens unit and
the second lens unit decreases and the separation between the second lens
unit and the third lens unit slightly increases. During the second zooming
operation, the separation between the second lens unit and the third lens
unit decreases.
In the numerical example 22 of FIGS. 36(A) to 36(C), during the first
zooming operation, the third lens unit remains stationary, the separation
between the first lens unit and the second lens unit decreases and the
separation between the second lens unit and the third lens unit increases.
During the second zooming operation, the separation between the second
lens unit and the third lens unit decreases.
In the numerical example 23 of FIGS. 37(A) to 37(C), during the first
zooming operation, the first lens unit and the third lens unit remain
stationary and the separation between the first lens unit and the second
lens unit decreases and the separation between the second lens unit and
the third lens unit increases. During the second zooming operation, the
separation between the second lens unit and the third lens unit decreases.
In the numerical examples 21 to 23, the refractive powers of the lens
units, similarly to the numerical examples 18 to 20, satisfy the
above-stated conditions (20) and (21). By this, all the aberrations are
made easy to correct, while still permitting the size of the entire lens
system to be minimized.
The technical significances of the conditions (20) and (21) are similar to
those of the above-stated conditions (16) and (17).
Again, in the numerical examples 21 to 23, similarly to the numerical
examples 15 to 17, for the medium focal length position (B) at which to
interchange the system between the zoom types and the telephoto end, the
lens systems have their paraxial refractive power arrangements determined
with every parameter satisfying at least one of the conditions (22) and
(23).
By this, a predetermined zoom ratio can be easily obtained while still
permitting the lens mounting mechanism to be simplified in structure. This
also leads to the realization of a zoom lens which is amenable to
much-desired increase of the maximum image angle while still permitting
the size of the entire system to be minimized.
The technical significances of the conditions (22) and (23) are similar to
those of the above-stated conditions (14) and (15).
FIGS. 38(A), 38(B) and 38(C) to FIGS. 40(A), 40(B) and 40(C) are schematic
diagrams of the paraxial refractive power arrangements of the numerical
examples 24 to 26 of the invention.
In these figures, L1 denotes the first lens unit of negative refractive
power; L2 the second lens unit of positive power; L3 the third lens unit
of positive or negative refractive power; and FP the image plane. Again,
FIGS. 38(A), 39(A) and 40(A) are in the wide-angle end; FIGS. 38(B), 39(B)
and 40(B) are in the medium focal length position; and FIGS. 38(C), 39(C)
and 40(C) are in the telephoto end. The arrows indicate the moving
directions of the lens units during zooming.
The numerical examples 24 to 26 each comprise, from front to rear, a first
lens unit of negative refractive power, a second lens unit of positive
refractive power and a third lens unit of negative refractive power,
totaling three lens units, wherein all the three lens units are moved
forward in differential direction to perform a first zooming operation
from the wide-angle end (A) to the medium focal length position (B). After
that, two of the three lens units are brought into unison, and the two
lens units and the other lens unit are moved forward in differential
relation to perform a second zooming operation from the medium focal
length position (B) to the telephoto end (C).
Especially, the first zooming operation is performed for each of the
numerical examples 24 to 26 of FIGS. 38(A) to 38(C) to FIGS. 40(A) to
40(C) by moving the first to third lens units forward in differential
relation.
The second zooming operation is performed by moving forward the first lens
unit and the third lens unit in unison for the numerical example 24 of
FIGS. 38(A) to 38(C), the first lens unit and the second lens unit in
unison for the numerical example 25 of FIGS. 39(A) to 39(C), or the second
lens unit and the third lens unit in unison for the numerical example 26
of FIGS. 40(A) to 40(C).
In the numerical example 24 of FIGS. 38(A) to 38(C), the differential
relation is such that, during the first zooming operation, the separation
between the first lens unit and the second lens unit decreases and the
separation between the second lens unit and the third lens unit decreases,
and that during the second zooming operation, the separation between the
first lens unit and the second lens unit decreases and the separation
between the second lens unit and the third lens unit increases.
In the numerical example 25 of FIGS. 39(A) to 39(C), during the first
zooming operation, the separation between the first lens unit and the
second lens unit decreases and the separation between the second lens unit
and the third lens unit increases. During the second zooming operation,
the separation between the second lens unit and the third lens unit
decreases.
In the numerical example 26 of FIGS. 40(A) to 40(C), during the first
zooming operation, the separation between the first lens unit and the
second lens unit decreases and the separation between the second lens unit
and the third lens unit increases. During the second zooming operation,
the separation between the first lens unit and the second lens unit
decreases.
Again, in the numerical examples 24 to 26, similarly to the numerical
examples 15 to 17, for the medium focal length position (B) at which to
interchange the system between the two zoom types and the telephoto end,
all the lens units have their paraxial refractive power arrangements
determined with every parameter satisfying at least one of the conditions
(24) and (25).
By this, a predetermined zoom ration can be easily obtained while still
permitting the lens mounting mechanism to be simplified in structure. This
also leads to the realization of a zoom lens which is amenable to much
desired increase of the maximum image angle, while still permitting the
size of the entire lens system to be minimized.
The technical significances of the conditions (24) and (25) are similar to
those of the above-stated conditions (14) and (15).
Next, the numerical data of the paraxial refractive power arrangements for
the numerical examples 15 to 26 of the invention are shown, where fi is
the focal length of the i-th lens unit; ei is the principal point interval
between the i-th lens unit and the (i+1)st lens unit; and sk is the back
focal distance. The values of the factors in the above-stated conditions
for the numerical examples 15 to 26 are listed in Table 3.
______________________________________
Numerical Example 15
f.sub.1 = -29.25
f.sub.2 = 23.10
f.sub.3 = -43.08
Focal length 36.00 82.90 101.99
of entire system
e.sub.1 20.15 7.81 7.59
e.sub.2 31.03 43.37 39.59
sk 17.31 30.72 46.30
Numerical Example 16
f.sub.1 = -38.16
f.sub.2 = 22.63
f.sub.3 = -35.00
Focal length 36.02 72.54 101.99
of entire system
e.sub.1 17.07 17.07 11.85
e.sub.2 29.08 16.12 17.16
sk 12.60 60.85 78.16
Numerical Example 17
f.sub.1 = -38.26
f.sub.2 = 22.71
f.sub.3 = -35.00
Focal length 36.01 84.84 101.99
of entire system
e.sub.1 23.83 9.76 7.61
e.sub.2 22.25 22.25 22.85
sk 22.12 51.50 60.16
Numerical Example 18
f.sub.1 = -40.68
f.sub.2 = 25.43
f.sub.3 = -36.87
Focal length 36.01 85.07 102.00
of entire system
e.sub.1 23.29 12.22 7.61
e.sub.2 32.80 28.41 33.19
sk 12.61 46.42 46.25
Numerical Example 19
f.sub.1 = -42.44
f.sub.2 = 26.29
f.sub.3 = -37.91
Focal length 36.00 85.01 102.00
of entire system
e.sub.1 25.38 12.38 7.63
e.sub.2 33.30 30.03 34.87
sk 12.90 44.52 44.52
Numerical Example 20
f.sub.1 = -42.09
f.sub.2 = 25.99
f.sub.3 = -37.33
Focal length 36.01 85.06 102.00
of entire system
e.sub.1 28.45 12.35 7.63
e.sub.2 29.26 29.26 33.98
sk 17.43 45.27 45.27
Numerical Example 21
f.sub.1 = -49.45
f.sub.2 = 25.32
f.sub.3 = -36.04
Focal length 36.04 69.43 101.96
of entire system
e.sub.1 22.74 7.63 7.63
e.sub.2 29.66 29.91 23.38
sk 12.59 27.45 57.20
Numerical Example 22
f.sub.1 = -43.53
f.sub.2 = 26.24
f.sub.3 = -37.17
Focal length 36.13 62.04 101.97
of entire system
e.sub.1 25.49 7.62 7.62
e.sub.2 32.62 44.15 33.40
sk 13.14 13.14 45.53
Numerical Example 23
f.sub.1 = -37.34
f.sub.2 = 25.87
f.sub.3 = -40.52
Focal length 36.01 66.31 101.96
of entire system
e.sub.1 23.58 7.61 7.61
e.sub.2 35.36 51.33 40.51
sk 12.57 12.57 41.12
Numerical Example 24
f.sub.1 = -40.03
f.sub.2 = 25.15
f.sub.3 = -36.39
Focal length 36.00 85.03 101.99
of entire system
e.sub.1 23.07 11.72 7.62
e.sub.2 32.24 28.74 32.84
sk 13.00 45.35 46.55
Numerical Example 25
f.sub.1 = -45.19
f.sub.2 = 23.61
f.sub.3 = -30.29
Focal length 36.00 83.00 101.99
of entire system
e.sub.1 25.38 7.63 7.63
e.sub.2 24.30 25.73 23.24
sk 17.71 38.54 54.29
Numerical Example 26
f.sub.1 = -39.43
f.sub.2 = 22.16
f.sub.3 = -28.99
Focal length 36.00 83.11 101.99
of entire system
e.sub.1 24.11 9.52 7.62
e.sub.2 22.03 22.87 22.87
sk 20.45 44.89 55.25
______________________________________
TABLE 3
______________________________________
Conditions
##STR11##
##STR12##
##STR13##
##STR14##
##STR15##
______________________________________
15 -0.012 -0.198 -- --
16 -0.177 0.035 -- --
17 -0.125 0.035 -- --
18 -0.272 0.282 0.97 0.21-0.23
19 -0.280 0.285 0.94 0.21-0.24
20 -0.279 0.279 0.95 0.21-0.23
21 0 -0.201 1.12 0.22-0.26
22 0 -0.269 0.95 0.17-0.22
23 0 -0.304 0.93 0.16-0.21
24 -0.242 -0.242 -- --
25 0 -0.131 -- --
26 -0.101 0 -- --
______________________________________
According to this embodiment, as is understandable from the foregoing, in
the 3-unit zoom lens preceded by the lens unit of negative refractive
power, the zooming range from the wide-angle end to the telephoto end is
divided into two regions of different zoom types, i.e., the first zooming
operation and the second zooming operation. In each of the zooming
regions, proper conditions for the movements of all the lens units are set
forth. Thus, a zooming method for the zoom lens is obtained that makes it
possible to form a lens mounting mechanism with the backlash lessened and
easily get the predetermined zoom ratio and to widen the maximum image
angle with ease.
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